1. Field of the Invention
The present invention relates to a filter, a duplexer, and a communication device for use in radio communication or the transmission/reception of electromagnetic waves, in e.g. a microwave band or a millimeter wave band.
2. Description of the Related Art
An example of a miniaturizable resonator for use in a microwave band or millimeter wave band is a spiral resonator, disclosed in Japanese Unexamined Patent Application Publication No. 2-96402. This spiral resonator is able to fit a longer resonance line in a given occupation area by forming the resonance line into a spiral shape, thereby achieving its overall size-reduction.
In such a conventional resonator, one half-wavelength line constitutes one resonator. Therefore, in a conventional resonator, the region where electrical energy is concentrated and stored, and the region where magnetic energy is concentrated and stored are separated from each other, and they are unevenly distributed at specified areas of a dielectric substrate. More specifically, the electrical energy is stored in the vicinity of an open end of the half wavelength line, while the magnetic energy is stored in the vicinity of the center portion of the half wavelength line.
Such a resonator constituted of one microstrip line has a drawback, in that characteristics thereof are inevitably subjected to deterioration caused by the edge effect which the microstrip line intrinsically possesses. Specifically, considering the line in cross-section, current is concentrated in the edge portions of the line (both ends in the width direction, and the upper and lower faces in the thickness direction of the line). Even if the film-thickness of the line is increased, the problem of power loss due to the edge effect inescapably occurs, since the edge portions at which the current is concentrated, can not be widened even if the film thickness of the line is increased.
In view of these problems, the present invention provides a resonator, a filter, and a duplexer which are capable of very effectively suppressing power loss caused by the edge effect, and which allow a greater reduction in overall size to be achieved. The invention also provides a communication device including the above-mentioned filter or duplexer.
In response to the above-described problems, the present invention, in a first aspect, provides a resonator comprising a plurality of line patterns, each of which is an aggregate of a plurality of lines, in each of which first and second ends of at least a portion of the plurality of lines are each disposed substantially at inner and outer periphery portions of the aggregate, around a predetermined point of a substrate, preferably symmetrically, and are disposed on the substrate so as not to intersect each other, in a mutually isolated state. In this resonator, each line of at least one of the plurality of line patterns has a spiral shape, and each line of at least one of the other line patterns has a pattern different from the line having a spiral shape.
In accordance with a second aspect, the present invention provides a resonator which resonates in a resonant mode of an integral multiple of a half-wave length. This resonator comprises a line pattern, which is an aggregate of a plurality of lines each having a spiral shape, in which first and second ends of at least a portion of the plurality of lines are each disposed substantially at inner and outer periphery portions of the aggregate, around a predetermined point of a substrate, preferably symmetrically, in which each of the inner and outer periphery portions of the line patterns is usable as a voltage opening end, and which are disposed on the substrate so as not to intersect each other. This resonator further comprises another line pattern which adds an electrostatic capacitance, utilizing the potential difference or a portion of the potential difference between the voltage node and the voltage antinode in the resonant mode. This other line pattern is disposed on a substrate in a state of being isolated from the above-described line pattern.
In the above-described plurality of spiral conductor patterns, spiral lines having substantially the same shapes are adjacent to each other. When microscopically seeing these spiral lines, physical edges exist in reality and weak edge effects occur at the edges of each of the lines. However, when macroscopically seeing the aggregate of these plural lines as one line, so to speak, the left edge of one line for example, is adjacent to the right neighborhood of another line which is congruent with the first line. That is, there are effectively no edges in the width direction of the lines. In other words, the existence of edges becomes insignificant. Utilizing this effect, the current concentration at edges of lines is very efficiently relieved and thereby the overall power loss is suppressed.
Furthermore, by disposing another line pattern adjacently to the line pattern in which each of the lines has a spiral shape, an electrostatic capacitance is equivalently added to the above-described line pattern constituted of spiral lines, whereby the resonant frequency is reduced, and by previously setting the line length of each of the spiral lines to be short, an overall size-reduction is achieved. Also, when forming line patterns having a given diameter, the loss reduction effect can be more enhanced by increasing the number of lines.
Preferably, at least one of the above-described plurality of line patterns is arranged, for example, radially.
It is preferable that each of at least two of the above-described plurality of line patterns be an aggregate of a plurality of spiral lines, and that the spiral directions thereof be opposite to each other. This allows the resonator to efficiently retain the magnetic-field energy by resonance and increases the Q value of the resonator.
In at least one of the above-described plurality of line patterns, preferably, portions which have substantially the same electrical potential in a resonant state are conductively connected. This effectively suppresses a spurious resonant mode.
It is preferable that at least one of the above-described plurality of line patterns is formed of a superconducting line. This increases the Q value of the resonator, allows sufficient low loss characteristics to be obtained, and enables the resonator to operate at a high Q value at a level not more than the critical current density.
Preferably, each of the line widths of the above-described plurality of line patterns is set to be substantially equal to the skin depth of the line conductor or narrower than the skin depth thereof, at an operating frequency. Thereby, the distance between the left and right inter-line gaps of a line becomes a distance such that the currents which flow in order to retain the magnetic flux passing through the gaps cause interference between left-side current and right-side one, and thereby reactive current having a phase deviated from the resonant phase is suppressed. This leads to a remarkable reduction in power loss.
In accordance with a third aspect, the present invention provides a filter which is formed by providing signal input/output portions to be connected to a resonator having any one of the above-described structures.
In accordance with a fourth aspect, the present invention provides a duplexer which is formed by providing one of the above-described filters as a transmitting filter or a receiving filter, or by providing one of the above-described filters as both a transmitting and a receiving filter.
The above-described filter or duplexer, allows a reduction in the insertion loss and an overall size-reduction to be achieved.
In accordance with a fifth aspect of the present invention, there is provided a communication device which is formed using the above-described filter or duplexer. This makes it possible to reduce the insertion loss at high-frequency transmission/reception portions, to improve communication qualities such as the noise characteristics and the transmission speed, and to reduce the overall size of this communication device.
The above and other features and advantages of the present invention will be clear from the following detailed description of the embodiments of the invention in conjunction with the accompanying drawings.